从ARM-GCC编译的elf文件中提取详细的符号信息(结构成员)

Question

我正在使用ARM-GCC 4.7.4为Cortex-M4编译代码。对于我们的调试工具，我需要以人类可读的格式(例如.txt)了解所有变量的名称、类型和地址。映射文件提供了大部分信息，不幸的是，下面的结构内容不是这样的：

typedef struct {    float32_t   Ref;        // Input:   Reference Value
            float32_t   Fdb;        // Variable:    Feedback Value
            float32_t   Err;        // Input:   Control Error
            float32_t   Kp;     // Parameter:   Gain of the Proportional Part
            float32_t   Up;         // Output:  Output of Proportional Part
            float32_t   Ki;     // Parameter:   Gain of the Integral Part
            float32_t   Ui;     // Output:  Output of the Integral Part
            float32_t   OutPreSat;  // Output:  Not saturated Output
            float32_t   OutMax;     // Parameter:   Maximum Output
            float32_t   OutMin;     // Parameter:   Minimum Output
            float32_t   Out;        // Output:  Saturated Output
        } PI_REG;

 PI_REG BU_Uctrl_Udc_PI_Reg = BU_UCTRL_UDC_PI_REG_INIT;

因此，我尝试使用工具nm、readelf和objdump从以dwarf-2格式使用参数-g3编译的.elf文件中获取一些信息。只有使用objdump我才能找到我搜索的信息：

objdump –Wi myfile.elf >symbols.txt

在symbols.txt文件中可以找到以下关于类型定义PI_REG的信息：

 <1><38883>: Abbrev Number: 2 (DW_TAG_base_type)
    <38884>   DW_AT_byte_size   : 4
    <38885>   DW_AT_encoding    : 4 (float)
    <38886>   DW_AT_name        : (indirect string, offset: 0x2c63e): float 
 <1><38891>: Abbrev Number: 11 (DW_TAG_typedef)
    <38892>   DW_AT_name        : (indirect string, offset: 0xb336d): float32_t
    <38896>   DW_AT_decl_file   : 4 
    <38897>   DW_AT_decl_line   : 370   
    <38899>   DW_AT_type        : <0x38883>
 <1><390d7>: Abbrev Number: 14 (DW_TAG_structure_type)
    <390d8>   DW_AT_byte_size   : 44    
    <390d9>   DW_AT_decl_file   : 6 
    <390da>   DW_AT_decl_line   : 26    
    <390db>   DW_AT_sibling     : <0x39176> 
 <2><390df>: Abbrev Number: 16 (DW_TAG_member)
    <390e0>   DW_AT_name        : Ref   
    <390e4>   DW_AT_decl_file   : 6 
    <390e5>   DW_AT_decl_line   : 26    
    <390e6>   DW_AT_type        : <0x38891> 
    <390ea>   DW_AT_data_member_location: 2 byte block: 23 0 (DW_OP_plus_uconst: 0) 
 <2><390ed>: Abbrev Number: 16 (DW_TAG_member)
    <390ee>   DW_AT_name        : Fdb   
    <390f2>   DW_AT_decl_file   : 6 
    <390f3>   DW_AT_decl_line   : 27    
    <390f4>   DW_AT_type        : <0x38891> 
    <390f8>   DW_AT_data_member_location: 2 byte block: 23 4 (DW_OP_plus_uconst: 4)

省略偏移量为6-32的结构杆件

 <2><39159>: Abbrev Number: 15 (DW_TAG_member)
    <3915a>   DW_AT_name        : (indirect string, offset: 0xc1d9a): OutMin    
    <3915e>   DW_AT_decl_file   : 6 
    <3915f>   DW_AT_decl_line   : 35    
    <39160>   DW_AT_type        : <0x38891>
    <39164>   DW_AT_data_member_location: 2 byte block: 23 24 (DW_OP_plus_uconst: 36) 
 <2><39167>: Abbrev Number: 16 (DW_TAG_member)
    <39168>   DW_AT_name        : Out   
    <3916c>   DW_AT_decl_file   : 6 
    <3916d>   DW_AT_decl_line   : 36    
    <3916e>   DW_AT_type        : <0x38891>
    <39172>   DW_AT_data_member_location: 2 byte block: 23 28 (DW_OP_plus_uconst: 40) 
 <1><39176>: Abbrev Number: 3 (DW_TAG_typedef)
    <39177>   DW_AT_name        : (indirect string, offset: 0xc00d0): PI_REG    
    <3917b>   DW_AT_decl_file   : 6 
    <3917c>   DW_AT_decl_line   : 37    
    <3917d>   DW_AT_type        : <0x390d7> 

 <1><3c348>: Abbrev Number: 29 (DW_TAG_variable)
    <3c349>   DW_AT_name        : (indirect string, offset: 0xc3ece): BU_Uctrl_Udc_PI_Reg
    <3c34d>   DW_AT_decl_file   : 1 
    <3c34e>   DW_AT_decl_line   : 40    
    <3c34f>   DW_AT_type        : <0x39176> 
    <3c353>   DW_AT_external    : 1 
    <3c354>   DW_AT_location    : 5 byte block: 3 fc 67 0 20 (DW_OP_addr: 200067fc)

如果我想获取有关变量的信息，例如结构BU_Uctrl_Udc_PI_Reg，我必须执行以下操作：

Find an entry called “DW_TAG_variable” and gather following information:
------------------------------------------------------------------------
 - DW_AT_name: The name is BU_Uctrl_Udc_PI_Reg
 - DW_OP_addr: Base address is 200067fc
 - DW_AT_type: The data type can be found at line 39176 

Search line 39176 and gather following information:
-----------------------------------------------------
 - It is a typedef (DW_TAG_typedef)
 - DW_AT_name: The typedef name is PI_REG
 - DW_AT_type: The definition can be found at line 390d7

Search line 390d7 and gather following information:
---------------------------------------------------
 - It is a structure (DW_TAG_structure_type) 
 - DW_AT_byte_size: It is 44 bytes wide

Search the structure Members in upcoming lines until 44 bytes are reached:
--------------------------------------------------------

1. Member (DW_TAG_member):
 - DW_AT_name: Ref
 - DW_AT_data_member_location: 200067fc + 0
 - DW_AT_type: The data type can be found at line 38891:
 - DW_TAG_typedef: float32_t
 - DW_AT_type: The data type can be found at line 38883: 
 - DW_TAG_base_type: float
 - DW_AT_byte_size: 4 bytes

2. Member (DW_TAG_member):
 - DW_AT_name: Fdb
 - DW_AT_data_member_location: 200067fc + 4
 - DW_AT_type: The data type can be found at line 38891:
 - DW_TAG_typedef: float32_t
 - DW_AT_type: The data type can be found at line 38883:
 - DW_TAG_base_type: float
 - DW_AT_byte_size: 4 bytes

[left out Members 3-9]

10. Member (DW_TAG_member):
 - DW_AT_name: OutMin
 - DW_AT_data_member_location: 200067fc + 36
 - DW_AT_type: The data type can be found at line 38891:
 - DW_TAG_typedef: float32_t
 - DW_AT_type: The data type can be found at line 38883:
 - DW_TAG_base_type: float
 - DW_AT_byte_size: 4 bytes

 11. Member (DW_TAG_member):
 - DW_AT_name: Out
 - DW_AT_data_member_location: 200067fc + 40
 - DW_AT_type: The data type can be found at line 38891:
 - DW_TAG_typedef: float32_t
 - DW_AT_type: The data type can be found at line 38883:
 - DW_TAG_base_type: float
 - DW_AT_byte_size: 4 bytes

坦率地说，脚本文件会比我的应用程序更复杂，因为它会自动收集上面提到的信息。此外，我必须承认，我真的不知道如何写这样的脚本。有没有更简单的方法来获取这种类型的信息？也许objdump有一些参数可以帮助我做到这一点，尽管我想我已经尝试了所有相关的参数？或者，是否存在能够做到这一点的工具？最后，我需要一个这样的表(另外，如果有所有的枚举就好了，当然也可以在.elf文件中找到)：

0x200067fc  float   BU_Uctrl_Udc_PI_Reg.Ref
0x20006800  float   BU_Uctrl_Udc_PI_Reg.Fdb
[…]
0x20006832  float   BU_Uctrl_Udc_PI_Reg.OutMin
0x20006836  float   BU_Uctrl_Udc_PI_Reg.Out

带有参数-- http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0477c/index.html的工具Fromelf text(包含在KeilµVision中)正好提供了这样一个表，但不幸的是，我不能使用它，因为它应该需要使用.elf，或者在本例中称为使用Arm编译器工具链编译的.axf文件。此外，还有许可证问题。

谢谢你的任何提示。

Answer 1

您应该能够要求GDB为您打印此信息，例如

gdb -q a.out
(gdb) ptype PI_REG

Answer 2

pahole是你需要的吗？它可以转储大小和偏移量的可变结构。

pahole −−reorganize −C foo xxx.out

struct foo {
int a; / 0 4 /
char c[4]; / 4 4 /
void b; / 8 8 /
long g; / 16 8 /
}; / size: 24, cachelines: 1 /
/ last cacheline: 24 bytes /
/ saved 8 bytes! /

Answer 3

您可以使用eclipse CDT的gdb mi接口以编程方式获取此信息。

private def loadElfFile(String elfFilePath) {
    var plugin = new MIPlugin

    var file = new File(elfFilePath)

    var cmdFactory = new CommandFactory("mi2")
    session = plugin.createSession(
        MISession::PROGRAM,
        'gdb',
        cmdFactory,
        file,
        #[],
        true,
        new NullProgressMonitor
    )
}

您可以在其中查询全局变量及其类型。地址存储在值的hexAddress属性中。

这种方法的问题是它的速度慢。一个有50个成员的结构几乎需要10秒来处理。查询所有结构需要几分钟的时间。对于IDE工具用例(如模型转换)，这是不切实际的。你必须深入潜水到精灵和矮人。